Sewing tube for a xenograft mitral valve

ABSTRACT

A mitral valve is removed from a pig heart with the annulus, leaflets, cordae tendineae and papillary heads intact. The porcine mitral valve is fixed. A covering material is attached to the papillary heads around the cordae tendineae. A sewing tube of a flexible material is attached to each of the papillary heads by sutures that extend through the covering material. The sewing tube extends away from the porcine mitral valve&#39;s papillary head remnants. A covering material is attached to the annulus. A human heart with a diseased or damaged human mitral valve is imaged in vivo to size the length between the mitral valve annulus and the papillary heads. The porcine mitral valve annulus to sewing tube length is adjusted to match the like dimension in the human heart by trimming the sewing tube. The human heart is opened and the mitral valve excised. The human heart&#39;s cordae tendineae are removed leaving the papillary heads intact. The porcine mitral valve is placed in the left ventricle and the sewing tubes are sutured to a respective papillary head. The mitral valve is sutured in place in the annulus and the human heart is closed.

This application is a division of application Ser. No. 08/566,229 filedDec. 1, 1995 which application is now U.S. Pat. No. 5,662,704.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to xenograft heart valves and more particularlyrelates to a porcine mitral heart valve for use in humans and the methodfor making and implanting the porcine mitral heart valve.

2. Description of Related Art

Heart valves from human cadavers, so called "homograft" valves, havebeen implanted in living human recipients for at least thirty years.Evolution of the Homograft Valve, Donald N. Ross, Special Presentation,Annals of Thoracic Surgery 59:565-7 (1995). A primary problem withhomograft valves is their availability. By contrast, heart valves fromanimals, so called "xenograft" valves, particularly from pigs, cows andsheep, are abundant. Porcine xenograft heart valves have been collected,treated and implanted in humans to replace damaged or defective humanheart valves since at least the early 1970s.

Porcine aortic heart valves have been found to be particularly goodreplacement heart valves for humans. One reason for this is that porcineheart valves have many similarities in both size and structure to thecorresponding heart valves in human hearts.

With respect to the mitral valve, a porcine mitral valve of a certainsize generally has cordae tendineae slightly shorter than the cordaetendineae of the human mitral valve it replaces. If a porcine mitralvalve of an annular size similar to the human mitral valve it replaceswere implanted in a human heart to replace a damaged or diseased humanmitral valve, the porcine cordae tendineae would probably not be longenough to reach the papillary heads in the left ventricle. If theporcine cordae tendineae were forced to reach the human heart'spapillary heads, undesirable stress would be placed on the subvalvularapparatus. This stress could cause the valve to deform and not performproperly. Alternately, the unnatural stress could cause the mitral valveto prematurely fail. Either of these results is therapeuticallyundesirable. Therefore, it is desirable in a xenograft mitral valve tomimic the distance from the endocardial wall through the papillarymuscles and the cordae tendineae to the annulus of the original humanmitral valve.

Throughout this disclosure, the term "subvalvular" means the part of theheart below the annulus of the mitral valve including the cordaetendineae and papillary heads and the term "annulus" means the part ofthe heart where the leaflets are inserted into the endocardium or innerwall of the heart. In addition, throughout this disclosure, "length ofthe cordae tendineae" means the distance from the endocardial wallthrough the papillary muscles and papillary heads, through the cordaetendineae to the annulus of the mitral valve when the mitral valve isimplanted.

Many factors can be used to choose the porcine mitral valve to beimplanted in the human. Many candidate porcine valves are rejectedbecause their shape, cosmetic appearance, or chordal distribution andgeometry are not desirable. However, for porcine mitral valves with thedesired shape, cosmetic appearance, and chordal distribution andgeometry, if the porcine mitral valve is chosen to provide theappropriate length cordae tendineae, the size of the mitral valve itselfwill generally be too large to fit the annulus presented from theexcised human mitral valve. These are problems in need of a solution.

A method for connecting the cordae tendoneae from an explanted xenograftmitral valve to the endocardial wall of a human heart has been tried byM. P. Vrandecic et al. Heterologous mitral valve transplant: the first50 patients clinical analysis, M. P. Vrandecic et al., European Journalof Cardio-thoracic Surgery, 9:69-74 (1995). Vrandecic's method allowsthe surgeon to tailor the chordal length of the xenograft from the humanmitral valve annulus to the endocardial wall where the papillary headsattach. However, Vrandecic's approach alters the three dimensionalstructure of the xenograft papillary head. Therefor, the xenograftpapillary head is subjected to unnatural stress which can lead tochordal rupture.

Herbert O. Vetter et al. have covered the severed papillary heads of amitral valve from a sheep with a patch of expandedpolytetrafluoroethylene (ePTFE) preparatory to implanting the valve inanother sheep. Mitral Allograft with Chordal Support: EchocardiographicEvaluation in Sheep, Herbert O. Vetter et al., Journal of Heart ValveDiseases, Vol. 4, No. 1, pages 35-39, January 1995. The severedpapillary heads are attached to truncated papillary muscles in the hostheart by sutures through the ePTFE material. Although the ePTFE materialprovided reinforcement for attaching the severed papillary heads to thetruncated papillary heads, this method also does not allow for thelength of the cordae tendineae to be lengthened as is required toimplant a porcine valve in a human heart and still preserve the humanheart's internal geometry.

Thus, the problem still exists as to how to lengthen the length of thecordae tendineae for a porcine mitral valve and maintain a physiologicstress distribution on the xenograft subvalvular apparatus that isimplanted into a human heart.

SUMMARY OF THE INVENTION

A mitral valve is removed from a pig heart with the cordae tendineae andpapillary heads intact. The porcine mitral valve is fixed. A coveringmaterial is attached to the papillary heads around the insertion of thecordae tendineae into the papillary heads. A sewing tube of a flexiblematerial is attached to each of the papillary heads by sutures thatextend through the covering material. The sewing tubes extend away fromthe annulus of the porcine mitral valve.

A human heart with a diseased or damaged human mitral valve ispreferably imaged in vivo to size the mitral valve and the length of thecordae tendineae. The sizing of the mitral valve may also be done invitro. The key aspect of the sizing, however done, is to accuratelymeasure the size of the human mitral valve and the length of the cordaetendineae in the human heart.

After the human mitral valve has been sized, the human heart is openedand the mitral valve excised. The cordae tendineae are also removedleaving the papillary heads intact. The sewing tubes on the porcinemitral valve are trimmed at their ends opposite their attachment to thepapillary heads so that the overall length of the porcine mitral valvefrom the trimmed edge of the valve's sewing tube to the valve's annulusmatches the length of the cordae tendineae measured previously in thehuman heart. The step of trimming the length of the sewing tubes can bedone either before or after the human mitral valve has been excised.

The porcine mitral valve is placed in the left ventricle and each sewingtube is sutured to a respective papillary head. The mitral valve issutured in place in the annulus and the human heart is closed followingnormal procedures for mitral valve repair or replacement as is wellunderstood by those skilled in the art.

It is a primary object of the invention to provide an implantableporcine mitral valve that maintains the correct relative orientation andgeometry of the various parts of the left ventricle and mitral valve.

It is another object of the invention to provide a xenograft mitralvalve that mimics the healthy native human mitral valve.

It is another object of the invention to provide an implantable porcinemitral valve that is adjustably attachable to the papillary heads.

It is another object of the invention to provide an implantable porcinemitral valve that is firmly attached to the papillary heads.

It is another object of the invention to provide an implantable porcinemitral valve that is easy to produce.

It is another object of the invention to provide an implantable porcinemitral valve that is easy to implant.

It is yet another object of the invention to provide an implantableporcine mitral valve that is strong and durable.

These and other objects of the invention will be clear with reference tothe attached drawings and the following detailed description of theinvention. Throughout this description, like elements, wherever referredto, are referenced by like reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cutaway view of a human mitral valve in position in a humanheart.

FIG. 2 is a cutaway view of a porcine mitral valve in position in a pigheart.

FIG. 3 is a perspective view of a porcine mitral valve ready for implantinto a human heart.

FIG. 4 is an inflow view of the porcine mitral valve of FIG. 3.

FIG. 5 is a perspective view of the connection of the cordae tendineaeto the sewing tube.

FIG. 6 is a perspective view of the rectangular piece of flexiblematerial from which a sewing tube is made.

FIG. 7 is a perspective view of the sewing tube.

FIG. 8 is a perspective view of human mitral valve in situ in a humanheart with stay sutures to mark reference points.

FIG. 9 is a cutaway view of the human left ventricle after the humanmitral valve has been removed and the papillary heads have been preparedto connect with the sewing tube of the porcine mitral valve of FIGS. 3through 5.

FIG. 10 is a cutaway view of the porcine mitral valve of FIGS. 3 through5 in the patient's left ventricle while the cordae tendineae are beingattached to the papillary heads.

FIG. 11 is a top cutaway view of the porcine mitral valve of FIGS. 3through 5 secured in position in a patient's annulus.

DETAILED DESCRIPTION OF THE INVENTION

A healthy human mitral valve is shown in FIG. 1 generally labeled 2within a human heart 4. Two sets of cordae tendineae 6a, 6b connectmitral valve 2 to corresponding papillary heads 8a, 8b within the leftventricle 10 of heart 4. Occasionally, the mitral valve 2 becomesdefective or injured and needs to be replaced. The invention is aporcine mitral heart valve for use in humans and the method for makingand implanting the porcine mitral heart valve.

A porcine mitral valve is shown in position in a pig heart in FIG. 2generally labeled 12. Valve 12 is prepared for implant into a human asfollows. The whole pig heart is collected shortly after the death of thepig. The left ventricle 14 and left atrium 16 of the pig heart issectioned and exposed thereby exposing the mitral valve 12, the cordaetendineae 18 and the papillary heads 20. Sectioning means cutting thepig heart in a plane parallel to the mitral valve annulus to open theleft atrium and bisect the septum and aortic valve to open the leftventricle without damaging the mitral valve.

The porcine mitral valve 12 is preliminarily fixed in situ by fixingportions of the left ventricle 14 and left atrium 16 containing themitral valve 12 by techniques well known in the art. These techniquesinclude but are not limited to low pressure glutaraldehyde fixing,aortic root pressure fixation or other tissue matrix preservingtechniques. The reason for this preliminary fixation in situ is topreserve the unique geometry of the mitral valve without requiring theentire heart to be fixed under pressure. However, the whole heart may befixed by applying pressure to the entire left heart in the presence of atissue fixation agent. Regardless of the way achieved, the key is to fixthe porcine mitral valve to render it non-immunogenic, biocompatible,and structurally stable.

In the initial fixation, the excess myocardium not integral to themitral valve 12 is used to maintain the unique geometry of the mitralvalve 12 while the mitral valve 12 is being fixed. After the initialfixation, the mitral valve maintains its shape. Thus, the excessmyocardium can be discarded.

The mitral valve 12 is excised from the pig heart remnant to include aportion of the endocardium 22 containing the papillary heads 20. Thepapillary heads 20 are excised close to the endocardium 22 so that foreach set of cordae tendineae 18 and papillary head 20, the entire cordaetendineae 18 and substantially the entire corresponding papillary head20 is removed.

In the preferred embodiment of the invention, the excised mitral valve12 is further fixed to complete fixation of the papillary heads 20.Then, the excess myocardial tissue is trimmed away and the mitral valve12 is stored in fixing solution to await further processing.

As is shown in FIGS. 3 and 4, an annular cover 24 is attached to annulus26 of mitral valve 12. Annular cover 24 is made of flexible material.Flexible material means a material that is suturable and conforms to theshape of the annulus 26. The desired characteristics of the flexiblematerial are that the material should be strong enough to allow theflexible material to be sutured to the annulus 26, be biocompatible andallow a normal healing response, that is, allow tissue to ingrow intothe material. The flexible material may be either synthetic orbiologically generated. The preferred material for the flexible materialis polyester made by Bard Vascular Systems under the brandname Dacron®and having a thickness of about 0.25 mm. Other material that could beused for the flexible material include, but are not limited to,polytetrafluorethylene (PTFE) or expanded polytetrafluorethylene (ePTFE)made by Meadox Medicals Inc. under the brand name Teflon® and GoreTex®,respectively, and pericardial tissue including bovine pericardialtissue.

The annular cover 24 is attached to annulus 26 by sutures so that thereare no exposed edges on the annular cover 24. If pericardial tissue isused as the material of the annular cover 24, the pericardial tissuemust be fixed. If the fixing process of the pericardial tissue doesn'tprovide anti-calcification, the pericardial material can be treated withan anti-calcification treatment.

A number of markers are preferably added to mitral valve 12 to aid inaligning mitral valve 12 in the human heart when mitral valve 12 isimplanted. These markers may include short axis markers 28, trigonemarkers 30, commisural markers 32 and markers 34 on sewing tubes 36 aswill be described hereafter. Markers 28, 30 and 32 preferably take theform of colored sutures. Markers 34 preferable are colored threads woveninto the material of the sewing tubes 36 at spaced intervals.

As shown in FIGS. 3 and 5, the remnants of the papillary heads 20 arecovered with a section 38 of flexible material. Papillary heads 20 arecovered by section 38 by suturing small pieces 40 of the flexiblematerial to the papillary heads 20 between the cordae tendineae 18. Itis preferable to avoid contact of the flexible material of section 38with the cordae tendineae 18 or their point of insertion into thepapillary heads 20. Individual small pieces 40 of the flexible materialare sewn together to form the entire section 38 of flexible material.Generally, it is desired to leave exposed a small ring of papillarytissue around the cordae tendineae 18 to avoid abrasion between thematerial of section 38 and the cordae tendineae 18. In this way, theflexible material of section 38 covers the entire remnant of thepapillary heads 20 and extends between the connecting points of thecordae tendineae 18 to the papillary heads 20.

Flexible material means a material that is suturable and conforms to theshape of the papillary heads 20. The desired characteristics of theflexible material are that the material should be strong enough to allowthe flexible material to be sutured to the remnants of the papillaryheads 20, be biocompatible and allow a normal healing response, that is,allow tissue to ingrow into the material. The flexible material may beeither synthetic or biologically generated. The preferred material forthe flexible material is polyester made by Bard Vascular Systems underthe brandname Dacron® and having a thickness of about 0.25 mm. Othermaterial that could be used for the flexible material include, but arenot limited to, polytetrafluorethylene (PTFE) or expandedpolytetrafluorethylene (ePTFE) made by Meadox Medicals Inc. under thebrand name Teflon® and GoreTex®, respectively, and pericardial tissue.

A sewing tube 36, as shown in FIGS. 3 and 5, is fashioned of a flexiblematerial. As shown in FIGS. 6 and 7, sewing tube 36 is formed from arectangular piece 42 of flexible material by sewing together the opposededges 44. This is preferably done by bringing together the opposed edges44 and directing the opposed edges 44 toward the interior 46 of thesewing tube 36 formed thereby. This produces a tube having no exposededges along the length of the sewing tube 36. The contact points 48, 50of the respective opposed edges 44 are then connected to each other by acontinuous suture 52 through sewing tube 36.

Preferably, the rectangular piece 42 used to form sewing tube 36 hasdimensions of from about 15 to 45 mm. by about 10 to 50 mm. Theresulting sewing tube 36 will then have dimensions of about 5 to 15 mm.in diameter and 10 to 50 mm. in length. Rectangular piece 42 alsopreferably has a thickness of about 0.25 mm. Colored markers 34 may beadded to rectangular piece 42 spaced regularly along rectangular piece42 so that when sewing tube 36 is created, markers 34 indicate lengthalong sewing tube 36 (FIG. 5).

The desired characteristics of the material of rectangular piece 42 areprimarily the same as those required for section 38. The material shouldbe strong enough to allow suturing without tearing, be biocompatible andallow fibrotic response, that is, allow tissue to ingrow into thematerial. The preferred material for rectangular piece 42 is Polyestersold by Bard Vascular Systems under the brandname Dacron®. Othermaterial that could be used for rectangular piece 42 include, but arenot limited to, polytetrafluorethylene (PTFE) sold by Meadox MedicalsInc. under the brand name Teflon® and pericardial tissue.

Sewing tube 36 is sutured directly to the remnant of the papillary head20 covered by section 38 so that sewing tube 36 extends away from mitralvalve 12. Sewing tube 36 provides a sewing surface to connect the humanheart's papillary heads 8 to the remnants of the papillary heads 20 ofthe porcine mitral valve 12. In this way, the length of the cordaetendineae can be adjusted to provide the correct fit for the geometry ofthe human heart 4. In other words, the use of sewing tube 36 allows thereplacement mitral valve 12, including cordae tendineae 18, to moreclosely approximate the geometry of the human mitral valve 2 with itscordae tendineae 6.

Before a xenograft porcine mitral valve 12 can be implanted in a human,the correct size for the mitral valve 12, including the length of thecordae tendoneae, must be determined. This sizing is preferably donewhile the heart 4 is beating. If the sizing is performed after the heart4 has been arrested, inaccurate measurements may result. This is becausethe heart 4 deflates and consequently changes its size when arrested andplaced on cardiopulmonary bypass. This change in size causes thedimensions of heart 4 to change. This sizing is preferably done througha trans-esophageal echo-Doppler exam (TEE) although other sizing methodsmay be used.

Once the sizing of the mitral valve 2, and consequently the replacementporcine mitral valve 12, has been determined, the damaged human mitralvalve 2 is removed from the human heart 4 by standard heart valvereplacement techniques as is well understood by those in the art.

Before mitral valve 2 is removed, stay sutures 54 (FIG. 8) are placed inthe tissue 56 surrounding mitral valve 2 to mark the trigones and shortaxis for geometric reference. These stay sutures 54 are usually ofdifferent colors and act as reference locations to match markers 28, 30and 32 on porcine mitral valve 12. The alignment of stay sutures 54 andmarkers 28, 30 and 32 allow the replacement porcine mitral valve 14 tobe correctly aligned in the human annulus 58 where mitral valve 2 wasremoved.

When the human mitral valve 2 is excised from the left ventricle 10, thecordae tendineae 6 are cut near the papillary heads 8. The cordaetendineae 6 are then trimmed to within about 2 mm around the remainingpapillary heads 8 (FIG. 9).

A number of plegeted sutures 60 are placed through the papillary heads 8(FIG. 9). Plegeted sutures 60 are used to distribute the stress on thesuture over a larger surface area on the papillary head 8 to aid indehisence prevention. Dehisence is tearing or ripping of tissue and canoccur when sutures are placed in tissue without support. The porcinemitral valve 12 with the attached sewing tube 36 is placed in the leftventricle 10 and aligned with the reference stay sutures 54 around thetissue 56.

Sewing tube 36 is trimmed in length to correspond to the measured lengthof the human papillary head 20 to annulus 58 dimension. This is done bycutting the end 62 of sewing tube 36 using markers 34 on sewing tube 36as a guide.

As shown in FIG. 10, the plegeted sutures 60 from each papillary head 8are sewn through a corresponding sewing tube 36 at a location on thesewing tube 36 to produce a desired length of the cordae tendoneae. Thesewing tubes 36 are slid down the plegeted sutures 60 into contact withthe papillary heads 8. The plegeted sutures 60 are then tied off therebysecuring the sewing tubes 36 to the papillary heads 8.

The porcine mitral valve 12 is placed in the patient's annulus 58 andaligned with the stay sutures 54. The porcine mitral valve 12 is thensewn into position in the annulus 58 using the stay sutures 54. Anyadditional sutures that may be needed to secure the mitral valve 12 inplace may be added.

The mitral valve 12 is then tested for competency. This is preferablydone by filling the left ventricle 10 with saline and checking aroundthe annulus 58 and at the mitral leaflet's line of coaptation 64 (FIG.4) for leaks. If leaks are found, additional sutures may be placedthrough the annulus 58 and mitral valve 12 to seal the leak.

Additional sutures may be placed at the junction of the sewing tube'sattachment to the human papillary head to adjust the leaflet's line ofcoaptation so as to prevent regurgitation. Once the mitral valve 12 issecurely and tightly positioned, the patient's heart 4 and chest cavityare closed by techniques well known in the art.

The use of sewing tubes 36 to connect the ends of the cordae tendineae18 and the papillary heads 8 to the remnants of the papillary muscles inthe human heart allows the physician more flexibility in adapting theunique geometry of the porcine mitral valve 12 to the unique geometry ofthe patient's heart 4. The use of sewing tubes 36 allows the physicianto adjust the length of the cordae tendineae. In addition, the use ofthe sewing tubes 36 allows the physician to maintain the unique geometryof the xenograft mitral valve 12. Allowing the xenograft mitral valve 12to retain its own unique geometry aids in preventing the valve 12 fromstructurally failing due to unnatural stresses that often result fromforcing the mitral valve 12 into an unnatural geometric configuration.

Although a sewing tube 36 made by sewing together the opposed edges 44of a rectangular piece 42 of flexible material has been disclosed as thepreferred embodiment, other types of sewing tubes 36 may be included inthe invention. For example, a sewing tube 36 formed of extruded ormolded material may also be used. In any alternate embodiment of thesewing tube 36, the key is that a flexible surface for adjustablyattaching the papillary heads 8 to the cordae tendineae 18 is provided.

The procedure described above is the preferred procedure for implantinga porcine mitral valve 12 in a human heart having internal leftventricular geometry not differing significantly from the norm. Thepresent invention allows the mitral valve 12 to be used even where theinternal left ventricular geometry differs significantly from the norm.This includes, but is not limited to, malpositioning of the papillaryhead or heads 20, cases where there is no distinct papillary headprotuberance from the endocardium, and cases where the normal attachmentpoint of the sewing tube 36 to the endocardium is calcified or necrotic.The invention allows the point of attachment of the sewing tube 36 tothe endocardium to be a selected by the surgeon at a physiologiclocation given the design of mitral valve 12, the patient's leftventricular geometry and the patient's disease state.

Although the invention has been described in connection with xenograftheart valves, the invention may also be practiced on homograft orartificial heart valves. The modifications necessary to the disclosedinvention to apply the invention to either a homograft or artificialheart valve will be clear to those skilled in the art.

The invention has been shown and described in connection with a specificembodiment. It is to be realized, however, that the description givenherein is for the purpose of illustrating the invention and is notintended to be limiting. It is further understood that improvements andmodifications to the disclosure made herein will occur to those skilledin the art and that such improvements and modifications will still fallwithin the scope of the invention.

What is claimed is:
 1. A sewing tube for a xenograft mitral valve madeaccording to the steps of:providing a piece of flexible material in theshape of a rectangle having opposed transverse edges; bringing togetherthe opposed transverse edges to form a mitral valve sewing tube havingan interior; directing the opposed transverse edges toward the interiorof the tube; and attaching the opposed transverse edges to each other.2. The sewing tube of claim 1 in which the rectangular piece of flexiblematerial has a transverse dimension of from approximately 15 toapproximately 45 mm and a longitudinal dimension of approximately 10 toapproximately 50 mm so that the tube is approximately 5 to approximately15 mm in diameter and approximately 10 to approximately 50 mm inlongitudinal length.
 3. The sewing tube of claim 1 in which therectangular piece of flexible material comprises visual indicatorsspaced along the rectangular piece.
 4. The sewing tube of claim 3 inwhich at least one visual indicator comprises a colored marker.
 5. Thesewing tube of claim 1 in which the rectangular piece comprisespolyester.
 6. The sewing tube of claim 1 in which the rectangular piececomprises polytetrafluorethylene.
 7. The sewing tube of claim 1 in whichthe rectangular piece comprises pericardial tissue.
 8. The sewing tubeof claim 1, in which the step of attaching comprises suturing at least aportion of the opposed edges to each other.